This invention is directed to a laser device having a closed envelope with a gaseous filling within the envelope. Because of the high operating temperature of the gaseous discharge within the envelope, the discharge is confined to a bore passage formed by a longitudinally extending array of carbon discs each having an aperture through its central portion. A cathode electrode is positioned adjacent to one end of the array of discs and an anode electrode is positioned at the opposite end to provide a gaseous discharge through the aligned apertures of the discs forming the bore. Reflectors at opposite ends of the bore provide with the bore an optical resonant cavity for the laser.
Laser devices of this type are filled with a suitable noble gas such as argon or krypton. The discharge through the bore provided by the aligned carbon discs is of a nature having a high current density often in the neighborhood of 500 amperes per square centimeter and may go as high as 1000 amperes per square centimeter, at gas pressures in the order of 1/10th of a torr. As described in U.S. Pat. No. 3,522,551, gas ion lasers of this type and operating within a high range of current density undergo a sputtering erosion of the carbon discs confining the discharge plasma, as well as a clean-up of the gas within the tube. The sputtering erodes the surfaces of the carbon discs forming the openings of the apertures extending through the carbon discs. The sputtered carbon is deposited within the central portions of the apertures between the openings, as well as on other surfaces within the envelope. The build-up of carbon within the central portions of one or more of the disc apertures forms a smaller bore for the plasma discharge. This, together with a drop in gas pressure results in an increase in the voltage drop across the discharge. The current density increases as well as the temperature and thermal dissipation through the carbon discs to the envelope of the tube. The reduction in the apparent bore size and hence of the laser beam causes excessive defraction loss and thus reduces the output beam of the device. These factors tend to shorten the lifetime of the tube.